1. Field of the Invention
The present invention relates to communication systems, and more particularly, to a communication system for exchanging communication data.
2. Description of the Related Art
In conventional network systems such as Ethernet (registered trademark) systems, control information relating to control of device operations, such as alarm/fault information and device status notification information, is generally transmitted by using part of channel resources allocated to user packets.
FIGS. 10A and 10B illustrate the concepts of how control information is transmitted in conventional systems. When control information is transmitted to a device within a network to control the device, the control information is assembled into a control information packet and inserted between user packets, as shown in FIG. 10A, or the control information is carried by the header of a packet, as shown in FIG. 10B.
As conventional techniques related to transmission of control information, a technique has been proposed in which control information is encoded and transmitted in such a manner that code words with neutral polarity and code words with non-neutral polarity do not exactly coincide in position (e.g., Japanese Unexamined Patent Publication No. 2002-217738 (paragraph nos. [00241] to [0029], FIG. 1)).
When control information is exchanged between devices in the conventional systems, however, part of the channel resources allocated to user packets is used to communicate the control information, as shown in FIGS. 10A and 10B, giving rise to a problem that the bandwidth available to users decreases by an amount corresponding to the control information.